PROJECT SUMMARY G protein-coupled receptor kinases (GRK) and arrestins act in concert to ensure rapid termination of G protein- mediated signaling by G protein-coupled receptors. Dopaminergic signaling via striatal dopamine receptors play a critical role in controlling multiple forms of behavior in the normal and diseased brain. Abnormalities of signaling by dopamine receptors have been strongly implicated in Parkinson's disease (PD) and motor complications caused by dopamine replacement therapy such as L-DOPA-induced dyskinesia. Dopamine receptors undergo GRK- and arrestin-dependent desensitization, and deficits in this process may underlie signaling abnormalities caused by the loss of dopamine or by dopaminergic drugs in PD. The lentivirus- mediated overexpression of GRK6 in the dopamine-depleted striatum normalizes behavior and dopamine receptor signaling in the rodent and primate animal models of PD, suggesting a critical role for GRKs in the regulation of dopamine receptors in the brain. This project is designed to explore the role of GRKs and arrestins in the dopaminergic regulation of behavior in live animals as well as fine molecular mechanisms of the GRK function in vivo. First Aim will examine specific roles of GRK isoforms in antagonizing L-DOPA- induced rotations and behavioral sensitization to L-DOPA in hemiparkinsonian rats. We will inject lentiviruses encoding wild type GRK isoforms, mutant GRKs with different functions selectively disabled, or GRK microRNAs to knockdown select isoforms into the dopamine-depleted striatum and test for rotational behavior following repeated L-DOPA administration. The Aim 2 is designed to test whether simultaneous overexpression of an arrestin and a GRK is more potent than overexpression of the same GRK alone in suppressing L-DOPA-induced motor symptoms. In Aim 3, we will examine the alterations in down-stream signaling pathways caused by perturbations in the GRK expression or function. In Aim 4, the feasibility of harnessing the receptor desensitization process to improve therapy in Parkinson's disease will be examined. The results of these experiments will help to sort out specific roles of GRK and arrestin isoforms in regulating dopaminergic signaling in the brain in vivo. The studies will pave the way to development of novel therapeutic approaches to control motor deficits in Parkinsons' disease and complications of L-DOPA therapy.